Phase velocity maps of the Taiwan region from the ambient noise tomography of the cross terms in Green’s function tensors

Based on the three-component continuous waveform data recorded by the 24 broadband seismic stations in the Broadband Array in Taiwan for Seismology （BATS） from January 2016 to June 2017, the empirical Green’s function tensors of surface waves are extracted by the cross-term correlation method. Rayleigh wave phase velocity maps from the period 6 s to 22 s are subsequently derived from cross-terms of the Green’s function tensors, which made good description of the crustal velocity structure in Taiwan region. Our results show that the Coastal plain and the Pingtung basin exhibit low-velocity characteristics, while the Western Foothills, Central Range and Coastal Range exhibit high-velocity characteristics in the short-period band. The low velocity zone shifts eastward gradually with period increasing. On the medium and long periods, velocities in southern and northern segments of Central Range are significantly low, indicating the northward and southward material extrusion related to the lithospheric collision between the Eurasian Plate and the Philippine Sea Plate. Besides, the velocities in the southern segment of the Central Rang are slightly lower than that of the northern segment, which may imply the more active southward extrusion. In addition, the high-velocity anomaly near the related depth in Taichung-Nantou area may indicate that the Penghu platform retains its relatively stable state since the Cenozoic Era during the extension and collision evolution of the northern margin of the South China Sea.